8 Puzzle
Moderate
ES PT-BR English RU

8 puzzle is a sliding puzzle that consists of a frame of randomly ordered, numbered square tiles with one missing tile. The object of the puzzle is to place the tiles in the right order (see picture) by using sliding moves to utilize the empty space. You can read more about this kind of puzzle on Wikipedia.

Our puzzle is presented as a 3x3 matrix with numbers from 1 to 8. Zero is the empty cell. You can "move" the empty cell in four directions: up--"U", down--"D", left--"L", and right--"R". You need to return a sequence of moves to solve the puzzle. The solution is presented as string of symbols ("UDLR") describing your moves.

Input: A matrix with numbers from 1 to 8 as a list of lists with integers.

Output: The route of the empty cell as a string.

Example:

```checkio([[1, 2, 3],
[4, 6, 8],
[7, 5, 0]]) == "ULDR"```

How it is used: The most obvious usage for the concepts in this task lie in creating a bot to solve slide puzzles; however, this task also is a fun way to learn something new because the n-puzzle is a classical problem for modeling algorithms involving heuristics.

Precondition:
len(puzzle) == 3
all(len(row) == 3 for row in puzzle)

Settings
Code:
CheckiO Extensions

CheckiO Extensions allow you to use local files to solve missions. More info in a blog post.

In order to install CheckiO client you'll need installed Python (version at least 3.8)

Install CheckiO Client first:

`pip3 install checkio_client`

Configure your tool

`checkio --domain=py config --key=`

Sync solutions into your local folder

`checkio sync`

(in beta testing) Launch local server so your browser can use it and sync solution between local file end extension on the fly. (doesn't work for safari)

`checkio serv -d`

Alternatevly, you can install Chrome extension or FF addon

`checkio install-plugin`
`checkio install-plugin --ff`
`checkio install-plugin --chromium`

Read more here about other functionality that the checkio client provides. Feel free to submit an issue in case of any difficulties.

Sync...